1. Field of the Invention
The present invention relates to a circuit board used in various electronic apparatuses.
2. Description of the Related Art
With a recent trend for a smaller size and a lighter weight of electronic apparatuses and a higher functionality thereof, there have been desired for such a circuit board that is smaller in size, lighter in weight, and higher in signal processing capability as well as mounting density. The manufacturing of such a circuit board that can meet these desires requires technologies for increasing the number of layers, decreasing the diameter of a via hole, and finer patterning of the circuits implemented thereon. Therefore, those desires have been extremely difficult to satisfy by a circuit board on which interlayer electrical connections are implemented by the conventional through-hole construction.
To meet those desires, new circuit boards have been developed. The materials of the circuit board have also included, besides the conventional glass-based materials, organic fiber-based materials and films on a trial basis.
One representative of such circuit boards employs a full-IVH construction in which the interlayer connection is implemented by conductive paste (see Japanese Patent Publication No. 2601128). This circuit board uses a composite material such as aramid-epoxy resin to form insulator layers thereof, to have such advantages as a smaller coefficient of thermal expansion, a lower dielectric constant, and a lighter weight, thus finding wide application in a variety of electronic apparatuses.
To further improve the functionality of the circuit board, however, it is necessary to secure the stability in its connection resistance for further prolonged period of time.